The present invention relates to a mold pin for forming a hole for a tire stud, a tire mold provided with the mold pins, and a method for manufacturing a tire by the use of the tire mold.
In general, a studded tire for use on ice is manufactured by firstly molding a pneumatic tire having stud holes and then driving tire studs in the stud holes.
As shown in FIGS. 7(a) and 7(b), the stud holes (d) are formed in the tread portion (c) during vulcanizing the tire by the use of mold pins (a) protruding from the inner surface of the tire vulcanizing mold (b).
The mold pin (a) is provided at the tip end thereof with an expanded portion (f) having a larger diameter than its main shaft portion (e) protruding from the mold (b).
Thus, the molded stud hole (d) has a constant diameter part (h) formed by the main shaft portion (e) and an increased diameter part (g) formed by the expanded portion (f).
As shown in FIGS. 8(a) and 8(b), an ice stud (i) is provided at one end of its main shaft portion (k) with a flange (j) having a larger diameter than the main shaft portion (k) so as not to drop out from the stud hole (d). The above-mentioned increased diameter part (g) of the stud hole (d) is formed to receive the flange (j).
From a standpoint of prevention of dropping out of a tire stud from a stud hole, it is preferred to increase the diameter difference between the increased diameter part (g) of the stud hole (d) from the constant diameter part (h) by increasing the diameter difference between the expanded portion (f) of the mold pin (a) from the main shaft portion (e).
However, if such diameter difference of the mold pin (a) is increased, it becomes difficult to pull out the mold pin from the vulcanized tire tread after the completion of the tire vulcanization, and there is a possibility that cracks are caused around the stud holes when demolding.